1. Field of the Invention
This invention relates to a digital processing apparatus and more particularly to a microprogrammed device for direct processing or emulation of a set of instructions through the use of a series of words stored in a control memory.
2. Description of the Prior Art
In the past, two separate types of microprogrammable processors have been in use, direct processors and emulation processors.
In the emulation processor one language code is used as an input code to point to macro subroutines comprised of microinstructions that simulate the intent of the input code. This type of microprogrammable processor can be divided into two parts: an outside processor which is typical of the classical variety processor and an internal processor which is typical of the direct microprocessor.
The direct microprogrammable processor is essentially a simple processor, mechanized as a device controlled by a control memory sub-system with microoperation codes strung together to form microinstructions that are general in nature.
Most processors and microprocessors utilize a multiple-phase clock and tend to be somewhat serial in operation. That is, in order to execute an instruction the device must fetch an instruction from a random access memory or a microcontrol memory, decode the instruction and generate the address of the operand to be used in execution of the instruction, extract the contents of the address referenced in the instruction, and finally execute the instruction.
In microprogrammed execution, some of the operations become more parallel, that is, the fetch and execute portion are complete in that when a microinstruction is fetched it is simultaneously decoded and the operation operands provided so that the instruction may be executed in the next clock cycle.